1. Field of the invention
This invention relates to improvements in an internal combustion engine of the split type operable on less than all of its cylinders when the engine is below a given value.
2. Description of the Prior Art
In general, internal combustion engines demonstrate higher efficiency and thus higher fuel economy when running under higher load conditions. In view of this fact, split type internal combustion engines have already been proposed which include split engine control means adapted to place the engine operation in a full engine mode where the engine operates on all of the cylinders at high load conditions and place some of cylinders out of operation to shift the engine operation into a split engine mode when the engine load is below a given level. This relatively increases active cylinder loads at low load conditions, resulting in higher fuel economy.
With split engine control means designed to place the engine operation in a split engine mode at idle conditions, however, a cold engine is started with operating only on the active cylinders, resulting in much time required for warming up the inactive cylinders. Thus, it occurs frequently to operate the inactive cylinders before they are not fully warmed up.
In order to eliminate this difficulty, an attempt has been made to force the engine operation to shift into a full engine mode for a predetermined time upon starting an engine even at idle conditions. However, this results in a fuel economy penalty. For example, if an engine is started again just after it is off, the engine operates in a full engine mode in spite of the fact that it is fully warmed up.
It is most preferable to force the engine operation to shift into a full engine mode even at idle conditions before the engine is fully warmed up for prompt engine warming and to shift the engine operation into a split engine mode at idle conditions after the engine is warmed up for minimized useless fuel consumption.